Old missed feature, by default the GMF-Runtime' outline uses somewhat weird rules of how to display editparts in the tree, and there is lack of generation support in GMF-Tooling for that.

We have a plan item for Luna https://bugs.eclipse.org/bugs/show_bug.cgi?id=417987 for this, so it would be a good place to discuss what are the "standard" requirements for "better" outline.
Also if you specify something about what you want to see in outline, I may explain how to deliver this in the manual code, until the #417987 is closed.